Get A Grip On Tire Selection - Radial or Cross-ply Tires? • Mick's Blog By Mick Farmer When I first came to Uganda, the choice of tyres was limited to either Firestone Translug or Firestone Translug! So, you were forced into a situation of having to pay over the odds for tyres that were, many times, unsuitable for the work that was expected of them. I was working for a project that was primarily operating in Southern Sudan, where the roads were poor, to say the least. This particular Firestone model, being a cross-ply (bias-ply) tyre was suited for the harsh demands of that environment. Cross-ply Tires Except for the generally low price, that is the only major advantage of a cross-ply / bias-ply tyre. The disadvantages include a strong and rigid sidewall. This causes the tyre to overheat when used on a sealed road surface and therefore, wear out quickly. When driven above 80 KPH cross-ply tyres will cause a vehicle to become unstable; this is because the tyres are trying to follow the natural lines of the road. Also, there is a risk of them exploding due to sever overheating.

Most vehicle manufacturers advise against fitting cross-ply / bias-ply tyres unless the vehicle is being used in an extremely harsh environment where sidewall strength is crucial. Radial Tires When Michelin invented the radial tyre it was hailed, and rightly so, as the biggest contributor to road safety of the last century. The radial has a substantial list of advantages, which include a flexible sidewall that gives good vehicle stability and its ability to maintain maximum contact patch with the road surface when cornering. Because of the inherent flexibility of the tyre, it doesn’t tend to overheat and therefore, lasts longer. BUT remember that each tyre type has a maximum speed rating that should not be exceeded! The disadvantages are; one, the relatively weak and, therefore, vulnerable sidewall and; two, the initial price. With regard to the latter, if you take into consideration that the tyre lasts longer if maintained correctly, you will actually save money in the long run and be safer on the road to boot. A win-win situation if ever there was one! On then to the vast, sometimes baffling selection of tyres now available to us in Uganda and what to choose.

You have to examine the type of work that your vehicle is going to do and what type of road surface / environment that the vehicle is going to be used on / in the majority of time. You should then pick a tyre to suit that environment. All Terrain Tires The all-terrain tyre has become very popular but you have to remember that this is a “jack of all trades and master of none” tyre. Whereas it’s overall performance is satisfactory, when it comes to the crunch it cannot compete with the specialist. The Differences Between Radial and Cross-Ply Tyres • Mick's Blog By Mick Farmer I was inspired to revisit this subject by a “late night” conversation with friends who had just fitted cross-ply tyres to their vehicles without realizing it. Many 4×4 owners still go for this option either for tradition, cost or just blind faith in the information given by the tyre dealer. In reality they are a false economy and they are not as safe as radial tyres.

Radial Tyres and Road Safety If we look at the history of tyres we find that all tyres were of cross-ply manufacturing process until Michelin invented the radial tyre process in the early 1970s; and if you remember the advert campaigns, they were deemed, by an ex police chief with a funny voice, as a “major contribution to road safety.”. He has subsequently been proven to be absolutely spot on with his statement. Understanding why this point is correct, is fundamental in understanding why we should refrain from fitting cross-ply tyres to our vehicles when they are going to be used for general and even fairly extreme off-road driving. Differences Between Radial and Cross-Ply Tyres The way that radial tyres are manufactured give them a flexible side wall whilst still retaining strength. This flexible sidewall allowed greater control over the direction of the tyre on the road and hence the vehicle went where you steered it without any hesitancy! Also, and of extreme importance, it allowed the tyre to retain its contact patch on corners rather than lean on a corner and lose contact. The cross-ply tyre has opposite qualities because it has a rigid sidewall.

This rigid sidewall and the general design of the tyre don’t allow heat to dissipate as effectively and the tyre wears out faster. Also, they don’t have a very high speed rating. Generally about 80 – 100 KPH. What this means is, if you drive in excess of this speed for over 4 hours you risk a blow out. This is why most vehicle manufacturers don’t recommend fitting cross-ply tyres onto their vehicles. How to Tell a Cross-ply Tyre from a Radial Tyre Then the question of how to recognize whether the tyre is one or the other arose. This is very straight forward. A common size of tyre for a 4×4 is 750 16. If it is written on the tyre 750R16 it means it is one of the good guys. The R standing for radial. If it doesn’t have the R, i.e. 750-16, then it’s one of the cheaper type. If it’s a profiled tyre such as 235/85R16 then it will be a radial.

Never Mix The Tyre Types The two types of tyre should never be mixed on a 4×4 (or on any other vehicle for that matter). If you think about it, if you do you have one type of tyre that has a mind of its own and tends to want to wander and the other that you have control over working against each other then this could lead to a dangerous loss of control. I have seen some folks carrying a cross-ply as a spare. If you are one of these then I would suggest changing it to suit the other four or if you have to use it then make sure you drive carefully until you can get the damaged one repaired. Are there Any Uses for Cross-Ply Tyres? Saying that, cross-ply tyres still have their place and generally can be fitted to vehicles that work in extremely harsh environments where there are no roads and the tyre risks getting side wall punctures from tree stumps or sharp rocks. As a side note, whatever tyre you decide to fit ensure that you follow the vehicle manufacturers’ recommendations for tyre pressures for that size and manufacturing process of tyre. Under inflated tyres are dangerous and can take off at least 20% off a tyres life.

Obviously wildly over inflated tyres are just as dangerous with the same effect on life span. Types of Tyre | Maxxis Tyres UK Tubeless (no tube required) or Tube type (requiring inner tube) All three construction types are manufactured in several tread profiles. Tread patterns and profiles are available for front and rear positions. Special tyres are available for sporting events, some of which are unsuitable for road use and are marked accordingly (normally NHS - Not for Highway Service). Mixing of tyres The intermixing of radial, bias belted and diagonal cross-ply tyres has legal requirements and motorcyclists are advised to consult the Motor Vehicles (Construction and Use) regulations obtainable from Her Majesty’s Stationery Office.

Recommended fitment: 1 Diagonal cross-ply front and rear 2 Diagonal cross-ply front and bias belted rear 3 Diagonal cross-ply front and radial rear 4 Radial front and rear 5 Bias belted front and rear Illegal fitment: 1 Radial front and diagonal cross-ply rear 2 Bias belted front and diagonal cross-ply rear 3 Radial front and bias belted rear Permitted Fitments Advantages and Disadvantages of Radial Tires - CarsDirect Advantages and Disadvantages of Radial Tires April 9, 2012 Learn the difference between radial tires and bias ply tires, and the pros and cons of each type. There are two classifications of tires: radial tires and bias ply tires. The classifications are based on a tire's construction and its features. A radial tire features transverse radial plies that run perpendicular to the direction of travel. This assures less heat buildup and a softer ride. Moreover, radial tires are manufactured with the plies laid radially which results in a more flexible tire wall. Bias ply tires are manufactured with the plies laid out diagonally, which causes the walls to not be as flexible.

Other elements of a radial tire along with each of their safety features include: A tread that protects the interior and assures high grip to the road. It is constructed to provide longer life as well as better maneuverability and durability. Steel belts that give stiffness to the tread. A spiral layer for higher durability and maneuverability. A thick shoulder that offers protection for the interior from shocks and damage. A flexible sidewall that protects the interior and offers a comfortable ride. A ply cord, which is the main body of the tire. It holds the inflation pressure and withstands load and road shocks. A bead filler which provides more durability and maneuverability. Bead wires which hold the tire to the rim. A chafer that protects the plycord from heat generated by the rubbing of the bead and rim flange. Radial Tire Advantages The advantages of radial tires over bias ply tires include: Flexible sidewalls. Reduced fuel consumption due to less rolling resistance. A softer ride because of the layout of the tire's plies and because of the flex of the sidewalls, assuring more stable contact with the road service and a softer ride. Less vibration. Extended tire life due to less heat generated by the tire.

Radial Tire Disadvantages The disadvantages of radial tires when compared to a bias ply tire include: Poor transport handling, since low lateral stiffness causes the tire sway to increase as the speed of the vehicle increases. Increased vulnerability to abuse when overloaded or under-inflated. The sidewall tends to bulge which could cause damage and puncture. A ply layout that causes the radial tire to follow a wheeltrack more consistently than a bias ply tire. The radial tire is more expensive than a bias ply tire which may be considered as a disadvantage. However, the radial tire lasts longer and this results in the savings of money over the long run. Related Questions and Answers How Does the Tire Tread Design on Radial Tires Differ from Others? Tire tread design varies significantly between radial tires and other types, including bias ply tires. Bias ply tires utilize a design in which the tire tread and sidewall of the tire share the same casing plies, which means the strength of both the tread and sidewall is compromised and dependent on each other. Radial tires have separate plies for the sidewalls and tread, which means that more of the tread is in contact with the road at all times.

The tread life is also improved with radial tires, as the stresses placed on the sidewall of the tire have less bearing on the condition of the treads. Is Tire Sidewall Repair More Difficult on Radial Tires? Yes, tire sidewall repair on radial tires is more difficult than on bias ply tires. While sidewall repair is common on bias ply tires, the fact that separate plies are used to form the sidewall of a radial tire makes it difficult to repair the sidewall. In fact, while tire sidewall repair on radial tires is possible, it is not recommended, as the sidewall of a radial tire is under more stresses than one on a bias ply tire. However, should you want to complete tire sidewall repair on a radial, it is possible using a traditional patch kit, although you should test the tire sidewall repair at low speeds before venturing on the freeway with your repaired tire. Is Radial Tire Repair More Extensive and Difficult than Other Tires? Yes, radial tire repair is more extensive and difficult than other tire repair types. Like those that might be encountered when repairing a bias ply tire on a boat trailer or similar.

As the sidewall and tread of a radial tire make use of separate plies, punctures that impact both areas must be handled as separate punctures, and separate plugs or patches must be applied. The easiest radial tire repairs to complete are those that must be made to the tread area or sidewall after a simple puncture caused by a screw, nail, twig or something similar. Making too many radial tire repair efforts without replacing a tire can result in a weakened tire that may be unsafe to use. Related Articles Clark Cars Tyre Safety TYPES OF TYRES In general there are 2 types of tyres. 1. Radial, 2. Diagonal (cross-) ply. Radial tyres may either be steel or textile braced, and are identified by the letter R in the size marking and usually the word "Radial". DON’T MIX TYRES Except in the case of temporary use spares it is illegal in the United Kingdom, and dangerous, to mix radial and cross-ply tyres on the same axle, or to have radial tyres on the front axle and cross-ply on the rear. KEEP UP THE PRESSURE Recommended tyre inflation pressures for your vehicle can be found either in the vehicle or tyre manufactures handbooks.

Correct pressures are related to loads, speeds and vehicle handling and are vital for even breaking, maximum grip and good tyre life. Prolonged under-inflation causes excessive flexing, deterioration of the casing, and rapid wear of the tread edges. Over-inflation results in an uncomfortable ride, a reduced tyre area of contact with the road surface and accelerated wear on the centre of the tread. Inflation must be checked at least once a fortnight and should only be checked when the tyre is cold, since there is an increase in pressure when the tyre has warmed up after being run. A reliable pressure gauge should be used. INSPECTION AND MAINTENANCE Tyres should be examined regularly, removing stones and other objects embedded in the tread. If the tyre has lumps or bulges it must be examined by a tyre specialist since they could indicate internal damage. Wipe away any oil or grease with a suitable diluted detergent. WATCH YOUR TREAD Tyre treads are designed to give good wet grip but the road surface condition plays a major part in tyre to road adhesion. In general, wet grip decreases as tyre tread patterns wear down or as the depth of surface water increases. Motorists should take this into consideration and reduce speed when it is wet.

Most car tyres have tread wear indicators in the tread grooves which show when the tyre is worn to 1.6mm remaining tread. The appearance of these indicators, level with the tread surface, should be taken as a sign that the tyre is ready for replacement. The legal limit of tread depth for car tyres in the United Kingdom is at least 1.6mm throughout a continuos band comprising the central three quarters of the breadth of tread and round the entire outer circumference of the tyre. TYRE LOAD AND SPEED MARKINGS Both radial and diagonal (cross-) ply tyres have markings to indicate their load and speed capabilities. It is important that tyres are suitable for the maximum speed at which the vehicle will be driven. In some overseas countries tyres are required by law to have a speed capability to match the vehicles maximum speed. New Tyres With certain exceptions, regulations in the United Kingdom require tyre speeds to be shown in accordance with an alphabetical list of symbols indicating speeds at 10km/h intervals. The relevant speed symbol is positioned near the size designation in conjunction with a load index number, e.g. 155R12 76S, where ‘76’ is the load index and S the speed symbol.

Details of speed and symbols are shown in tables 1 and 2. It is important that the tyre load capacity is adequate. Retreaded Tyres Under revised UK regulations introduced in 1988, retreaded tyres will be speed rated in the same way as new tyres. Prior to the introduction of these regulations, retreaded tyres are required to perform a minimum of 70mph. Tyres Tyres branded ‘Regraded Quality D.A.’ are capable of the same speeds as new tyres of the same type and size. How to Determine If Your Tires are Run-Flats - Tire Talk & Improve Vehicle Performance By Colin | Tire Rack How to Determine If Your Tires are Run-Flats Friday, May 3, 2013 by Colin . Run-flat tires have become standard equipment on many vehicles. Some cars of the same general model will have certain versions that come with run-flats while others do not. It can certainly get confusing for people who aren't familiar with different vehicle and tire models. All run-flat tires have a designation on the sidewall that indicates they are not standard tires.

For example, the Bridgestone Potenza RE960AS Pole Position has a run-flat and non-run-flat model in certain sizes. The run-flat model has the letters "RFT" following the name. You can see this by clicking on the Bridgestone Potenza RE960AS Pole Position RFT photo below. Radial or crossply tyres | The Late Bay Radial or crossply tyres Was about to buy new tyres for my trailer but then I notice "use code xxxx for crossply tyre option " !my current tyres dont state which they are. So Which dfo I buy? I just remember those ads from thee 70s about putting crossply and radial tyres on the same azxcle on your maxi with funny conseqsuences FAQs FAQs Frequently Asked Questions ALL SPECIAL OFFERS OR DISCOUNTS ARE MUTUALLY EXCLUSIVE - A CUSTOMER CANNOT APPLY MORE THAN ONE DISCOUNT OR OFFER TO AN ORDER. FOR GIVEAWAY OFFERS, THE OFFER APPLIES TO THE FIRST ORDER PLACED DURING THE OFFER PERIOD ONLY. How can I convert my tyre pressures from bars to psi? From bars to psi multiply by 14.5034.

From psi to bars multiply by .06895 (or divide by 14.5034) How do I calculate the revolutions per mile of my tyres? To obtain the true figure you should take the deflection into account and start with the diameter (in inches) less tread height. Therefore the calculation should be; tyre diameter (less 2x tread depth), multiplied by 3.142 to get the circumference, you should then divide 63360 (which is the number of inches per mile) by the circumference to obtain the revolutions per mile. Why can't I run my Beaded Edge tyres at a lower pressure for a more comfortable ride? Beaded edge tyres are "inflation held" unlike more modern tyres, they stay on the rim by air pressure alone. Reducing the pressure could allow the tyre to "jump off" the rim or lead to rapid tyre failure as the tyre chafes against the rim. Why do my crossply tyres develop "flatspots" when I leave my car parked for a few days? As the vehicle travels along, the tyres rotate and flex. This action generates heat within the casing of the tyre as the cords move.

When the vehicle stops the weight of the car presses down in one place and the tyre's cool down, this can sometimes cause the tyre to "set" or develop a temporary flat spot. During the next drive the tyre warms up again and the process is repeated. To stop or significantly reduce this cycle, raise the tyre pressures by 2 or 3 psi this reduces the flexing and therefore reduces the heat generated. My car has wire wheels but I can't find tube type tyres, so can I put tubes in my tubeless tyres? Most manufacturers accept that it is safe to fit tubes in tubeless tyres providing the correct size tube is used. Can you offer guidance on the use of tubes in tubeless road tyres? When tubes are fitted, it is important for the user to understand the potential drawbacks. When a tube is fitted to any tyre, it is important that the inside of the tyre is carefully examined to ensure that there is no feature which could cause premature tube failure due to cuts or chafing. Such examples are:- Any tire manufacturer’s paper or plastic identification labels must be removed and label indentations buffed smooth.

Damage to the inside of the tyre, possibly due to a previous penetration or repair can lead to chafing of the tube and subsequent failure. The following points should be noted: Inner tubes must be fitted to all tyres that are NOT marked as “Tubeless” and to all tyres marked as “Tube Type”. Always use a new tube in a tyre with matching size marking. Inner tubes should also be used: Where tubeless tyres are fitted to non-safety wheels or multi-piece wheels. Where tubeless tyres are fitted with wire spoked wheels where air could otherwise escape through the spoke holes in the wheel. Inner tubes should not be used as a means of repairing a puncture to a tubeless tyre, as a proper repair should be carried out to retain the tubeless properties of the tyre. The fitment of tubes to tyres of 65 series and lower is not recommended. If correct size tubes are not available, an alternative size tube should NOT be used. Wire wheels, multi-piece wheels and some single piece wheels designed for tube type applications CANNOT be used as tubeless fitments and the use of a tube (regardless of whether the tyre is “tube type” or “tubeless”) is ESSENTIAL FOR SAFETY.

Always use tubes in such fitments. My crossply tyres have several size markings on them, why is this? Some crossply tyres are dual marked, for example 475/500-19, this means that the tyre will replace both a 475-19 and a 500-19. It is therefore a compromise between the two. Why can't I use treaded racing tyres on my road car? There are several reasons why this is not advisable, racing tyres are built without compromise; they are generally a softer rubber so may not last long and could overheat, they have reduced wall and crown thickness to reduce weight and could be easily damaged. Racing tyres are also moulded with reduced tread depth offering limited water clearance. Can I mix radial and crossply tyres on my car? For the best performance keep the same construction of tyre on front and rear but yes, you can mix the two. By law you have to fit crossply on the front and radial on the back. Is it possible to fit modern radials on my 60's classic car?

In some cases you can replace crossply tyres with radials - but it is not always the best option and the tyre should be selected carefully - contact us for advice. I am fitting radials in place of crossply tyres on my car - should I keep the tyre pressure the same? No -when fitting radial tyres in place of crossplys it is normally important to increase the tyre pressure due to the difference in construction. The difference in pressure can vary, so it is very important you contact us for advice when changing to radial tyres. One of my beaded edge tyres recently came off the rim and I noticed it was quite rusty inside, are they safe? The shape of the rim shares a high level of importance with the pressure, the nose at the tip of the clinch intrudes into the tyre forming a positive lock. However if this area is allowed to develop a sharp corroded edge it will rapidly cut the tyre bead. It is also common practice amongst restorers to cut this area back to provide a more sympathetic surface. This is a mistake and will lead to premature failure as it drastically reduces the support in this area.

My car is fitted with new beaded edge tyres but both front tyres have bulges on the sides, is this fault with the tyre? From your description I suspect that the heel of the tyre has actually torn, leaving the side wall unsupported resulting in a side wall bulge. This is commonly caused by one of two reasons, the first and most common is under inflation, this allows the tyre to flex on the rim which in turn allows the nose of the rim to chafe and eventually cut through the toe. The second reason is poor rim condition, over the years it has become common practice to "cut back" or "tidy up" the nose on the rim edge to remove the sharp corroded edge, this is not good practice as it leaves the heel of the tyre unsupported when under load causing the rim to "skin off" the tyre heel. I need to replace a tyre on my car but I can't find a local garage that can help, the tyres are 820x120 beaded edge. I can understand tyre dealers and garages expressing concern as they are quite different from modern tyres. However, with a little advice and care it is possible to fit them yourself.

Firstly with the tyre removed check the rim for condition if necessary we can provide a copy of the rim profile, check for crushed clinches, sharp and corroded edges etc. Slightly inflate the tube and with some French chalk fit the tube inside the tyre. Offer the tyre to the rim and put the valve in the valve hole. With a beaded edge tyre lever, lever on the inside bead first, taking care to avoid pinching the tube, beaded edge tyres are like giant elastic bands so expect some resistance! When your satisfied that the first side is on correctly, work around the rim with the lever, you will find it easier with two levers at this point, one to hold the beginning in place and one to work around. With the tyre fitted rotate the tyre while bouncing on the ground to ensure the heels fit into the clinches correctly, when your satisfied that the tyre is fitted correctly inflate the tyre to 5psi, stop and check correct heel fitment and inflate to correct pressure. Beaded edge lever have hooks at one end to avoid" tube nipping". What are the approximate rim dimensions for beaded edge tyres? The chart below gives approximate dimensions for the rims designed for beaded edge tyres.

The size and condition of your rims is of the utmost importance when using this tyre design - please contact us with any questions. RIM SIZE Types Of Tires: All-Terrain Tires, Snow Tires, And Run-Flat Tires Types Of Tires Types Of Tires TYPES OF TIRES Your tires were specifically chosen for your vehicle to handle a variety of driving and weather conditions. This careful attention to detail makes your tires one of the most important safety features on your car, truck, or crossover. Different types of tires can perform better or worse—depending on conditions—so it’s important to understand how they work. Check your Owner’s Manual for information regarding your tire warranty or visit the Certified Service expert technicians for more help. VIEW TIRE OFFER ALL-TERRAIN TIRES All-terrain tires provide good performance on most road surfaces, in most weather conditions, and for off-road driving. The tread pattern on these tires may wear more quickly than others. Consider rotating these tires more frequently than the recommended 7,500 miles if you notice irregular wear. Check your tire wear here . RUN-FLAT TIRES Run-flat tires can be driven on with no air pressure. There is no need to stop to change the tire.

Continue driving, but not too far or too fast. Driving on the tire may not be possible if there is permanent damage. To prevent permanent damage, keep speeds below 50 mph. PERFORMANCE TIRES Performance tires are designed for enhanced handling under demanding circumstances and generally have high-speed ratings with a low aspect ratio for improved control. These tires are not built for winter conditions. ALL-SEASON TIRES All-season tires are for year-round use and feature a blend of technologies that make use of different compounds and detailed tread configurations, designed for most driving conditions such as snow, rain, heat, cold, etc. These tires offer good overall performance on most road surfaces and in most weather conditions. SUMMER-ONLY TIRES Summer tires have a special tread and compound that are optimized for maximum dry- and wet-road performance. This special tread and compound will decrease performance in cold climates and on ice and snow. NOTE: Do not use summer tires in winter conditions, as it would adversely affect vehicle safety, performance, and durability. Use only GM-approved tire and wheel combinations. Unapproved combinations may change the vehicle’s performance. Learn more about important tire and wheel information at your dealer.

SNOW/WINTER TIRES Winter tires are designed for increased traction on snow- and ice-covered roads. Consider installing winter tires if frequent driving on ice- or snow-covered roads is expected. See your dealer for details regarding winter tire availability and proper tire selection. With winter tires, there may be decreased dry-road traction, increased road noise, and shorter tread life. After changing to winter tires, watch for changes in the vehicle’s handling and braking. If you decide to use snow/winter tires: • Use tires of the same brand and tread type on all four wheel positions. • Use only radial ply tires of the same size, load range, and speed rating as the Original Equipment tires. • Winter tires with the same speed rating as the Original Equipment tires may not be available for H, V, W, Y, X, Z, and R speed-rated tires. If winter tires with a lower speed rating are chosen, never exceed the tires’ maximum speed capability. Auto Maintenance Car Bibles : The Wheel and Tyre Bible Dieselgate continues with Jeep I'm not sure why this took so long to come out - I wrote about Jeep's diesel cheating problem on October 19th 2015 - 15 months ago.

But sure enough, it's finally come to light this week that yes - Jeep have the problem too. So now we're just waiting for the other ten to be named : Mazda, Honda, Mitsubishi, Mercedes Benz, Renault, Nissan, Hyundai, Citroen, Fiat and Volvo. I'm honestly not sure why it's taking so long. Emission Analytics proved the diesel vehicles from all those manufacturers emitted way higher NOx levels than stated, which means in order to pass any sort of smog or emissions test, they must have some sort of defeat code or device in them. I suppose that now Trump is in charge, and now the EPA is going to be run by climate-denier Scott Pruitt, those other ten manufacturers will probably be let off the hook. The wheel and tyre Bible - everything you need to know about how to read your tyres (tires) and wheels with more info on rim sizes, tread depth and wear, aquaplaning, wheel balancing, aftermarket wheels, alloys, TPMS tire pressure monitoring systems and much more. The Wheel & Tyre Bible Are you confused by your car tyres, or if you're American, your tires? Don't know your rolling radius from your radial?

Then take a good long look through this page where I hope to be able to shift some of the mystery from it all for you. At the very least, you'll be able to sound like you know what you're talking about the next time you go to get some new tyres. How to read your tyre markings This is probably the number one question I get asked - "how do I read my tyre markings?". It's confusing isn't it? All numbers, letters, symbols, mysterious codes. Actually, most of that information in a tyre marking is surplus to what you need to know. So here's the important stuff: How to read your tire markings Key North American Dept of Transport compliance symbols and identification numbers. H Country of manufacture. As well as all that, you might also find the following embossed in the rubber tyre marking: The temperature rating - an indicator of how well the tyre withstands heat buildup. "A" is the highest rating; "C" is the lowest. The traction rating - an indicator of how well the tyre is capable of stopping on wet pavement. "AA" is the highest rating; "C" is the lowest. The tread-wear rating - a comparative rating for the useful life of the tyre's tread.

A tyre with a tread-wear rating of 200, for example, could be expected to last twice as long as one with a rating of 100. Tread-wear grades typically range between 60 and 600 in 20-point increments. It is important to consider that this is a relative indicator, and the actual life of a tyre's tread will be affected by quality of road surfaces, type of driving, correct tyre inflation, proper wheel alignment and other variable factors. In other words, don't think that a tread-wear rating of 100 means a 30,000 mile tyre. Encoded in the US DOT information (G in the tyre marking above) is a two-letter code that identifies in detail where the tyre was manufactured. In other words, what factory and in some cases, what city it was manufactured in. It's the first two letters after the 'DOT' - in this case "FA" denoting Yokohama. This two-letter identifier is worth knowing in case you see a tyre recall on the evening news where they tell you a certain factory is recalling tyres. Armed with the two-letter identifier list, you can figure out if you are affected.

It's a nauseatingly long list, and I've not put it on this page. But if you click here it will popup a separate window with just those codes in it. Another useful resource, which I discovered by myself is CARiD.com. Huge selection of tires, plenty of useful videos and articles and the most accurate wheel & tire fitment database in the industry: You just select the year, make and model of your vehicle, choose the right diameter, offset, backspacing, and bolt pattern and wait for your new set of tires to arrive! Additional markings In addition to all of the above, here is a comprehensive list of other markings you can find on your sidewall. This section is hidden by default because it takes up a lot of space on the page. the additional markings section. SSR: Continental Self Supporting Runflat ZP: Michelin Zero Pressure OE Manufacturer Letters In the same way that Porsche specifies N-rated tyres (see later), there's even more markings on the sidewall of a tyre that can denote tyres fitted as original equipment (OE) to various makes of vehicle. In some cases, the 'preferred' OE tyres are slightly different than the same-named tyres without the OE specification.

For example on some Honda SUVs, the tyres that are stamped with 'DZ' have a lower rolling resistance tread pattern than those that aren't. In true "Keeping the customer confused" fashion, you'll notice that (F) is not the same as (f). Go (f)igure. The following table shows all the letters assigned to OE tyres for various manufacturers. This section is hidden by default because it takes up a lot of space on the page. the OE manufacturer letters section. Code Mazda / Toyota DOT Codes and the 6-year shelf life As part of the DOT code (G in the tyre marking above), there is a tyre manufacture date stamped on the sidewall. Oddly this code is sometimes only one one sidewall so you might need to get under your car and look at the inward-facing side of the tyre. Take a look at yours - there will be a three- or four-digit code. This code denotes when the tyre was manufactured, and as a rule-of-thumb, you should never use tyres more than 6 years old. The rubber in tyres degrades over time, irrespective of whether the tyre is being used or not.

When you get a tyre change, if you can, see if the tyre place will allow you to inspect the new tyres first. It's not uncommon for these shops to have stuff in stock which is more than 6 years old. The tyre might look brand new, but it will delaminate or have some other failure within weeks of being put on a vehicle. Reading the code. The code is pretty simple. The three-digit code was used for tyres manufactured before 2000. So for example 1 7 6 means it was manufactured in the 17th week of 6th year of the decade. In this case it means 1986. For tyres manufactured in the 90's, the same code holds true but there is a little triangle after the DOT code. So for this example, a tyre manufactured in the 17th week of 1996 would have the code 176 After 2000, the code was switched to a 4-digit code. Same rules apply, so for example 3 0 0 3 means the tyre was manufactured in the 30th week of 2003.

DOT tire code Check your spare I had a reader email me about the age code and he pointed out that it's wise to check your spare tyre too. In his case, he had an older vehicle but his running tyres were all nice and fresh. It was his spare that was the problem - it had a date code on it of 081 meaning it was manufactured in the 8th week of 1991. At the time of writing, that was a 16 year old tyre. So you've been warned - if you're driving an older car, check the date code of your spare. If you get a flat and your spare is gently corroding in the boot (or trunk), it won't do you much good at all. DOT Age Code Calculator The calculation built in to this page is up-to-date based on today's date. If the DOT age code on your tyres is older than this code, change your tyres. DOT AGE CODE: Interesting note : in June 2005, Ford and GM admitted that tyres older than 6 years posed a hazard and from their 2006 model year onwards, started printing warnings to this effect in their drivers handbooks for all their vehicles.

Take the age code seriously : a tale of caution A reader contacted me in 2010 with a tale of caution regarding the manufacturing age code on old tyres. In August 2010, I bought a classic 1976 Mercedes with only 30,000 miles on it. The seller (who was only the second owner) warned me that he thought that the Michelin XVS tyres were pretty old (the spare was unused). I was aware of the dangers of old tyres from reading your tyre bible, but it was a Sunday and the tyres are an unusual size (205/70R14) and were not readily available. I thought that I'd risk the trip back home (250 miles), but that I'd need to get new tyres ASAP. Unfortunately, one of the tyres didn't last that long, and failed at 70 MPH (see photo, note my skidmarks). It turned out that the tyres were date-stamped from week 30, 1986(!), so the advice about old tyres is indeed true! For the record, I ordered new tyres and had the minor body damage repaired, and all is well with the car now.

Stephen W, Dublin, Ireland. The E-Mark Item F in the tyre marking diagram above is the E-mark. All tyres sold in Europe after July 1997 must carry an E-mark. The mark itself is either an upper or lower case "E" followed by a number in a circle or rectangle, followed by a further number. An "E" (upper case) indicates that the tyre is certified to comply with the dimensional, performance and marking requirements of ECE regulation 30. An "e" (lower case) indicates that the tyre is certified to comply with the dimensional, performance and marking requirements of Directive 92/33/EEC. The number in the circle or rectangle denotes the country code of the government that granted the type approval. 11 is the UK. The last number outside the circle or rectangle is the number of the type approval certificate issued for that particular tyre size and type. Tyre size notations Okay, so you look at your car and discover that it is shod with a nice, but worn set of 185-65HR13's (from the tyre marking). Any tyre mechanic will tell you that he can replace them, and he will.

You'll cough up and drive away safe in the knowledge that he's just put some more rubber on each corner of the car that has the same shamanic symbols on it as those he took off. So what does it all mean? tire size markings This is the width in mm of the tyre from sidewall to sidewall when it's unstressed and you're looking at it head on (or top-down). This is known as the section width. This is the ratio of the height of the tyre sidewall, (section height), expressed as a percentage of the width. It is known as the aspect ratio. In this case, 65% of 185mm is 120.25mm - the section height. This is the speed rating of the tyre. This tells you that the tyre is a radial construction. Check out tyre construction if you want to know what that means. This is the diameter in inches of the rim of the wheel that the tyre has been designed to fit on. Don't ask me why tyre sizes mix imperial and metric measurements. They just do. Okay? More recently, there has been a move (especially in Europe) to adjust tyre designations to conform to DIN.

This is the German Institute for standardisation - Deutsches Institut fuer Normung, often truncated to Deutsche Industrie Normal. DIN sizing means a slight change in the way the information is presented to the following: Section width Speed rating . Ultra high speed tyre size notations There is a subtle difference in the notation used on ultra high speed tyres, in particular motorcycle tyres. For the most part, the notation is the same as the DIN style described above. The difference is in the way the speed rating is displayed. For these tyres, if the speed rating is above 149mph, then a 'Z' must appear in the dimension part of the notation, as well as the actual speed rating shown elsewhere. The 'Z' is a quick way to see that the tyre is rated for over 149mph. Section width Speed rating . Classic / vintage / imperial crossply tyre sizes What ho. Fabulous morning for a ride in the Bentley. Problem is your 1955 Bentley is running on 7.6x15 tyres. What, you ask, is 7.6x15? Well it's for older vehicles with imperial measurements and crossply tyres.

Both measurements are in inches - in this case a 7.6inch tyre designed to fit a 15inch wheel. There is one piece of information missing though - aspect ratio. Aspect ratios only began to be reduced at the end of the 1960s to improve cornering. Previously no aspect ratio was given on radial or crossply tyres. For crossply tyres, the initial number is both the tread width and the sidewall height. So in my example, 7.6x15 denotes a tyre 7.6 inches across with a sidewall height which is also 7.6 inches. After conversion to the newer notation, this is the equivalent to a 195/100 15. If you're plugging numbers into the tyre size calculator lower down this page, I've included an aspect ratio value of 100 for imperial calculations. Note: I put 195/100 15 instead of 195/100R15 because technically the "R" means radial. If you're trying to get replacement crossply tyres, the "R" won't be in the specification.

However if you're trying to replace your old crossply tyres with metric radial bias tyres, then the size does have the "R" in it. Here is a javascript calculator to turn your imperial tyre size into a radial metric tyre size: Your imperial tyre size: Equivalent standard tyre size is : /100 R For quick reference, you could also try my vintage tyre size conversion table which lists a lot of common sizes along with their modern counterparts. classic tire sizes Classic / vintage radial tyre sizes Remember above that I said aspect ratios only started to come into play in the 1960s? Unlike the 100% aspect ratio for crossply tyres, for radial tyres, it's slightly different - here an aspect ratio of 80% is be assumed. So for example, if you come across on older tyre with 185R16 stamped on it, this describes a tyre with a tread width of 185mm and a sidewall height which is assumed to be 80% of that; 148mm. The question of the aspect ratio for radial sizes has been the subject of a lot of email to me.

I've had varying figures from 80% up to 85% and everyone claims they're right. Well one reader took it to heart and did some in-depth research. It seem there is actually no fixed standard for aspect ratio when it is not expressly stated in the tyre size. Different manufacturers use slightly different figures. The english MOT (road-worthiness test) manual states: Unless marked otherwise, "standard" car tyres have a nominal aspect ratio of 82%. Some tyres have an aspect ratio of 80%. These have "/80" included in the size part of the tyre marking e.g. 165/80 R13. Note: Tyres with aspect ratios of 80% and 82% are almost identical in size and can be safely mixed in any configuration on a vehicle. See for the online version. If you're plugging vintage radial numbers into the tyre size calculator, I've included aspect ratios of 80 and 82 for these calculations.

Alpha numeric load-based tyre sizes for vintage cars Picture credit: Jensen Intercepter Club On some 60's and 70's era vintage vehicles, (for example the Jensen Interceptor), the tyre sizes were denoted as ER70VR15. The '70' refers to the section height as you might expect, and the '15' is the wheel dimension, but on first inspection there appears to be no section width. Actually there is, but it's in yet another odd format. In this case, the first letter is the thing to look at. The letter itself has no direct equivalent to modern dimensional sizes but instead relates to load index; the higher the letter the more load it can carry. With vintage tyres, higher loads translated into bigger tyres, so the close approximations between old load and new size these days are: C = 185 D = 195 E = 205 F = 215 G = 225 H = 235 etc. In this example then, ER70VR15 means 205/70 R15 with a 'V' speed rating.

Whilst many of the latter Interceptors were technically capable of 140mph, the aerodynamic behaviour would have you quickly backing off to about 120mph so frankly that 'V' rating is a little optimistic. If you're looking to replace tyres for this type of vehicle, an 'H' speed rated tyre is the better choice, and it's cheaper. For those of you reading this in the colonies, an example vehicle from this era is the Chevy Nova which had E78-14 tyres. (In this case, there was no letter 'R' meaning these were cross-ply tyres, not radials). The equivalent size in modern notation would be 205/78 R14. The following converter will give you a rough idea of the equivalent metric tyre size for a given alpha numeric tyre size: Your alphanumeric tyre size: / R For quick reference, you could also try my vintage tyre size conversion table which lists a lot of common sizes along with their modern counterparts. Metric Tyre sizes and the BMW blurb Fab! You've bought a BMW 525TD. Tyres look a bit shoddy so you go to replace them. What the....?

TD230/55ZR390? What the hell does that mean? Well my friend, you've bought a car with metric tyres. Not that there's any real difference, but certain manufacturers experiment with different things. For a while, (mid 1990s) the 525TD came with arguably experimental 390x180 alloy wheels. These buggers required huge and non-conformal tyres. I'll break down that classification into chunks you can understand with your new-found knowledge: TD - ignore that. 230 = cross section 230mm. 55 = 55% sidewall height. Z=very high speed rating. R390=390mm diameter wheels. These are the equivalent of about a 15.5" wheel. There's a nice standard size for you. And you, my friend, have bought in to the long-raging debate about those tyres. They are an odd size, 180x390. Very few manufacturers make them now and if you've been shopping around for them, you'll have had the odd heart-stopper at the high price.

The advice from the BMWcar magazine forum is to change the wheels to standard sized 16" so there's more choice of tyres. 215-55R16 for example. The technical reason for the 390s apparently is that they should run flat in the event of a puncture but that started a whole debate on their forum and serious doubts were expressed. You've been warned... If you're European, you'll know that there's one country bound to throw a spanner in the works of just about anything. To assist BMW in the confusion of buyers everywhere, the French, or more specifically Michelin have decided to go one step further out of line with their Pax tyre system. See the section later on to do with run-flat tyres to find out how they've decided to mark their wheels and tyres. Metric tire sizes Land Rovers and other off-road tyre sizes On older Land Rovers (on the LWB/110 vehicles and many "off-roaders"), you'll often find tyres with a size like 750x16. This is another weird notation which defies logic. In this case, the 750 refers to a decimalised notation of an inch measurement.

750 = 7.50 inches, referring to the "normal inflated width" of the tyre - i.e. the external maximum width of the inflated, unladen tyre. (This is helpfully also not necessarily the width of the tread itself). The 16 still means 16 inch rims. Weird eh? The next question if you came to this page looking for info on Land Rover tyres will be "What size tyre is that the equivalent of in modern notation?". Simple. It has no aspect ratio and the original tyres would likely be cross-ply, so from what you've learned a couple of paragraphs above, assume 100% aspect ratio. Convert 7.5inches to be 190mm. That gives you a 190/100 R16 tyre. (You could use the calculator in the section on Classic / vintage / imperial crossply tyre sizes above to get the same result.) Generally speaking, the Land Rover folks reckon a 265/65R16 is a good replacement for the "750", although the tread is slightly wider and might give some fouling problems on full lock.

It's also 5% smaller in rolling radius so your speed will over-read by about 4mph at 70mph. If you can't fit those, then the other size that is recommended by Landrover anoraks is 235/85R16. On Discoveries, Range Rovers, or the SWB Defenders/Series land rovers you'll find "205" tyres, denoting 205mm x 16 inches. The 205 type tyres can generally be replaced with 235/70R16 or 225/75R16. The 235 is a wider tyre and the general consensus in Land Rover circles is that it holds the road better when being pushed. If you're really into this stuff, you ought to read Tom Sheppard's Off Roader Driving (ISBN 0953232425). It's a Land Rover publication first published in 1993 as "The Land Rover Experience". It's been steadily revised and you can now get the current edition from Amazon. I've even helpfully provided you with this link so you can go straight to it....

LT (Light Truck) imperial tyre sizes Confused yet? Okay how about this: 30x9.5 R15 LT or LT30x9.5/15. Yet another mix-and-match notation, this time for (amongst other things) light truck classification tyres. All the information you need to figure out a standard size is in there, but in the usual weird order. In this case the 30 refers to a 30 inch overall diamter. The 9.5 refers to a 9.5 inch wide tread. The R15 refers to a 15 inch diameter wheel. In order to figure out the closest standard notation, you know the tread width which (in this example) is 9.5 inches or 240mm. The sidewall height is the overall height minus the wheel diameter all divided by 2. So 30 inches minus 15 inches, which gives you 15 inches. Half that to get 7.5 inches and that's the sidewall height - 190mm.

Remember the section value is a percentage of the tread width - in this case 190mm/240mm gives us a section of 80% (near enough). So the standard size for 30x9.5R15 works out to be 240/80R15. In truth you can barely find a tyre that size so most off-roaders with that sort of tyre size go for 245/70R15 which is more common. For your convenience, another calculator then. Your LT tyre size: Light truck tires Porsche N-rated tyres Porsche designs and manufacturers some of the highest performance cars in the world (with the exception of the butt-ugly Cayenne). All this design and performance is worth nothing if you put cheap Korean tyres on your Porsche, and because of that prospect, Porsche introduced the N rating or N specification system. In order for a manufacturer to be an OE (original equipment) supplier of tyres for Porsches, they must work with the Porsche engineers at the development and testing stage. They concentrate on supreme dry-weather handling but they also spend a considerable amount of time working on wet-weather handling.

Porsches are typically very tail-heavy because of the position of the engine relative to the rear wheels, and with traction control off, it's extremely easy to spin one in the wet. Because of this, Porsche specify a set of wet-grip properties which is way above and beyond the requirements of any other car manufacturer. OE tyres for Porsches must successfully pass lab tests to prove that they would be capable of adequately supporting a Porsche at top speed on a German Autobahn. Once the lab tests are done, they must go on to track and race tests where prototypes are evaluated by Porsche engineers for their high-speed durability, uniformity and serviceability. If they pass all the tests, Porsche give the manufacturer the go-ahead to put the car tyres into production and then they can proudly claim they are an N-rated Porsche OEM (Original Equipment Modifier). The N-ratings go from 0 (zero) to 4, marked as N-0, N-1 etc. This N-rating, stamped into a tyre sidewall, clearly identifies these tyres as having gone through all the nauseating R&D and testing required by Porsche as described above. The number designates the revision of the design.

So for a totally new design, the first approved version of it will be N-0. When the design is improved in some way, it will be re-rated as an N-1. If the design changes completely so as to become a totally new tyre, it will be re-rated at N-0. If you've got a Porsche, then you ought to be aware that as well as using N-rated tyres, you ought to use matching tyres all around because many Porsches have different sizes tyres front and rear. So for example if you have a Porsche with N-3 rated tyres and the rear ones need replacing but the model has been discontinued, you should not get N-0's and put them on the back leaving the old N-3's on the front. You should replace all of them with the newer-designed re-rated N-0 tyres. But then you own a Porsche so you can certainly afford four new tyres.... One final point. You may go into a tyre warehouse and find two tyres with all identical markings, sizes and speed ratings, but one set has an N-rating. Despite everything else being the same, the non-N-rated tyres have not been certified for use on a Porsche.

You can buy them, and you can put them on your car, but if you stuff it into the armco at 150mph, Porsche will just look at you and with a very teutonic expression ask why you didn't use N-rated tyres. Porsche tires Like the site? The page you're reading is free, but if you like what you see and feel you've learned something, a small donation to help pay down my car loan would be appreciated. Thank you. Lies, Damn Lies and Speed ratings All tyres are rated with a speed letter. This indicates the maximum speed that the tyre can sustain for a ten minute endurance without coming to pieces and destroying itself, your car, the car next to you and anyone else within a suitable radius at the time. Speed Symbol 240+ 150+ 'H' rated tyres are the most commonplace and widely used tyres, having replaced 'S' and 'T' ratings. Percentage-wise, the current split is something like this: S/T=37%, H=63%, V=8%. Certain performance cars come with 'V' or 'ZR' rated tyres as standard.

This is good because it matches the performance capability of the car, but bad because you need to re-mortgage your house to buy a new set of tyres. A note on the ZR rating: most speed ratings designate the speed that should not be exceeded. For example W-rated tyres are rated up to 270km/h. ZR-rated tyres, by comparison, are theoretically rated for anything over 240km/h. This is why the Bugatti Veyron was shod with ZR-rated tyres for the world record speed run of 431km/h when Top Gear drove it at the VW Ehra-Lessien test track. Although to be honest, at that speed the tyres only lasted for 8 minutes. UTQG Ratings The UTQG - Uniform Tyre Quality Grade - test is required of all dry-weather tyres ("snow" tyres are exempt) before they may be sold in the United States. This is a rather simple-minded test that produces three index numbers : Tread life, Traction and Temperature. The tread life index measures the relative tread life of the tyre compared to a "government reference".

An index of 100 is equivalent to an estimated tread life of 30,000 miles of highway driving. The traction test is a measure of wet braking performance of a new tyre. There is no minimum stopping distance, therefore a grade "C" tyre can be very poor in the wet. The temperature test is run at high speeds and high ambient temperatures until the tyre fails. To achieve a minimum grade of "C" the tyre must safely run at 85mph for 30 minutes, higher grades are indicative of surviving higher speeds (a rating of "B" is, for some reason, roughly equivalent to a European "S" rating, a rating of "A" is equivalent to an "H" rating.) There are some exceptions: Yokohama A008's are temperature rated "C" yet are sold as "H" speed rated tyres. These UTQC tests should be used only as a rough guide for stopping. If you drive in the snow, seriously consider a pair of (if not four) "Snow Tyres". Like life, this tyre test is entirely subjective. Load indices The load index on a tyre is a numerical code associated with the maximum load the tyre can carry.

These are generally valid for speed under 210km/h (130mph). Once you get above these speeds, the load-carrying capacity of the tyre decreases and you're in highly technical territory the likes of which I'm not going into on this page. (Mostly because I don't understand it). The table below gives you most of the Load Index (LI) values you're likely to come across. For the sake of simplicity, if you know your car weighs 2 tons - 2000kg - then assume an even weight on each wheel. 4 wheels at 2000kg = 500kg per wheel. This is a load index of 84. The engineer in you should add 10% or more for safety's sake. For this example, I'd probably add 20% for a weight capacity of 600kg - a load index of 90. Generally speaking, the average car tyre is going to have a much higher load index than you'd ever need.

It's better to have something that will fail at speeds and stress levels you physically can't achieve, than have something that will fail if you nudge over 60mph with a six pack in the trunk. LI kg

Question: Radial, Crossply, and Run-flat are all types of what?
Answer: Tyres